#include <iostream>
#include <iomanip>
#include <ctime>
using namespace std;

int main()
{
    int n, m;

    while (cin >> n >> m)
    {
        //double t1 = clock();
        if (n==0 && m==0) break;

        double ans = 0;
        for (int i=n; i<=m; ++i)
        {
            ans += 1.0/(i*i);
        }
        //double t2 = clock();
        cout << fixed << setprecision(5) << ans << endl;
        //cout << "time = " << fixed << setprecision(2) << (double)(t2-t1)/CLOCKS_PER_SEC << endl;
    }

    return 0;
}
